This invention relates to methods and apparatus for the fabrication of objects.
In the current competitive domestic, industrial and military markets, the commercial lifetimes of products are continually decreasing and their design complexity is increasing. This has led to an ever-increasing need for rapid prototyping technology in the manufacturing industries. Rapid prototyping has already demonstrated its ability to reduce a product""s development time, and to allow manufacturers to react faster and more flexibly to meet the demands of the rapidly changing markets.
At present, there are various types of commercially available rapid prototyping methods, such as (a) selective laser curing of liquid monomers, usually within a pool of the liquid (Stereo lithography, SLA) [see publication reference 1], (b) selective laser sintering (SLS) of powders (e.g. polymers, resin coated metal and sand) [1] and (c) layer object manufacturing (LOM) [2] which involves the laser cutting and adhesive bonding of sheets of papers or slip casting of ceramic tapes. These methods have been used to produce prototypes of new designs for evaluation and testing. In addition, they have successfully produced patterns for casting or plastic moulding tools needed for the manufacturing of prototypes of design products or short run products.
However, the parts that are made by these methods always suffer from low mechanical strength due to poor density or excessive resin, and so require additional process steps such as debinding of resin, and heat treatment for densification. This may lead to undesirable shrinkage resulting in poor dimensional control. In addition, these methods are limited to a selected range of materialsxe2x80x94generally being limited to use only with polymers.
In the SLA method, the monomers are photosensitive and have a low storage lifetime, leading to a high cost of the precursor materials.
In the SLS method, the surface finish quality of the final part is constrained by the size of the powder, and often a subsequent machining step is needed to give an acceptable surface finish.
In the LOM technique, the dimensional control is limited due to staircase-edge effect caused by the stacking of the sheets.
There is therefore a need for a rapid prototyping technology capable of producing fully dense and functional parts directly from a computer-aided-design (CAD) model without the need for the time wasting intermediate processing steps. There is also a need for a technique which will allow other, possibly stronger or otherwise more suitable, materials to be used in rapid prototyping.
Reference [5] discloses a fabrication method involving photocurable plastic sheets, whereby regions of the sheets are cured by application of a laser beam. A technique for producing 3-D objects from a powder precursor has been proposed [6], with a vibration wiper blade being used to help apply the powder to a recipient surface. A stereolithography method involving polymer resin cured by a laser beam [7] uses an electric or magnetic field used to align particles within the polymer. Fabrication techniques in [8] and [9] make use of a gaseous precursor.
A fabrication method in which an object is formed as a plurality of successive laminae, the method comprising the repeated steps of:
(i) applying a sol precursor onto a recipient surface;
(ii) providing a temperature gradient along an application path of the precursor, so that the precursor is heated as it approaches the recipient surface and a sol-gel transition is initiated so that a gel layer is deposited on the surface; and
(iii) locally heating regions of the gel layer by directing a light beam onto those regions of the deposited precursor, so that the locally heated regions transform to a solid material.
This invention also provides fabrication apparatus for fabricating an object as a plurality of successive laminae, the apparatus comprising:
(i) a precursor outlet for applying a sol precursor onto a recipient surface;
(ii) a heater for providing a temperature gradient alone an application path of the precursor, so that the precursor is heated as it approaches the recipient surface and a sol-gel transition is initiated so that a gel layer is deposited on the surface; and
(iii) a directable light beam for locally heating regions of the deposited precursor so that the locally heated regions transform to a solid material.
This invention provides a new rapid prototyping process (embodiments of which will be referred to herein as laser gel manufacturing (LGM)) capable of efficiently producing high quality engineering parts, especially ceramic components for manufacturing industries.